474  PRE-CAMBRIAN    GEOLOGY    OF    NORTH    AMERICA. 
blendic,  or  dolomitic,  with  altered  slates  and  true  conglomerates  and 
limestones. 
4.  Granites  and  diorites,  some  of  which  are  clearly  intrusive  and 
newer  than  the  rocks  which  they  penetrate. 
Between  the  basement  granite  gneiss  and  the  overlying  Hastings 
series  there  is  sometimes  an  apparently  fairly  regular  sequence; 
at  other  times  the  limestone  of  the  Hastings  series  occurs  in  bands 
intimately  associated  with  the  granite  gneiss,  while  occasionally 
the  schists  rest  upon  this  lower  rock.  From  the  fact  also  that  the 
lower  gneiss  is  apparently  of  igneous  origin,  while  the  members  of 
the  upper  series  are  of  sedimentan^  character,  or  at  least  large  por- 
tions of  these  may  be  assigned  to  this  category,  an  unconformity 
may  be  assumed.  It  would  appear  from  the  examination  of  the 
Hastings  series  over  widely  separated  areas  that  there  is  a  marked 
resemblance  at  many  points,  and  that  in  fact  most,  at  least  of  the 
limestones  and  associated  schists,  with  gneiss,  are  repeated  from  point 
to  point,  forming  basins  of  approximately  the  same  horizon. 
Adams  and  Barlow,55  in  1906,  map  and  describe  the  portion  of 
the  protaxis  lying  to  the  north  of  Lake  Ontario.  In  this  district 
there  is  a  typical  development  of  Logan's  Grenville  series.  The 
area  mapped  is  extensive,  embracing  about  4,000  square  miles,  and 
was  shown  to  be  underlain  by  a  series  of  stratified  or  stratiform 
rocks  consisting  chiefly  of  crystalline  limestones  with  subordinate 
bodies  of  amphibolite  and  certain  gneisses  probably  of  sedimentary 
origin.  These  are  invaded  by  masses  of  granite  and  granite  gneiss 
which  northward  constantly  increase  in  number  and  extent  until 
they  run  together  and  pass  into  the  great  and  continuous  body  of 
Laurentian  gneiss  which  forms  the  mass  of  the  northern  protaxis 
of  the  continent. 
These  granite  gneiss  intrusions  have  the  form  of  batholiths,  around 
which  the  sedimentary  rocks  sweep  in  a  series  of  curves  and  between 
which  they  settle  down.  The  granite  batholiths  adjacent  to  the 
intruded  strata  hold  scattered  through  them  fragments  of  the  Gren- 
ville formation,  which  become  smaller  and  less  numerous  on  re- 
ceding from  the  contact.  This  gneiss,  however,  when  the  cover  has 
been  completely  removed,  displays  a  foliation  strike,  which  when 
traced  out  shows  a  series  of  lines  curving  around  certain  centers, 
which  mark  the  foci  of  batholithic  intrusion.  The  limestone  series, 
where  it  is  invaded  by  the  granite,  is  on  the  margin  fretted  away 
into  a  species  of  filigree  work,  and  becomes  at  the  same  time  very 
highly  altered. 
There  is  distinct  proof  that  under  the  influence  of  this  invading 
granite  the  limestone  in  some  places  has  been  changed  into  an  am- 
phibolite, practically  indistinguishable  from  that  produced  by  the 
dynamic  alteration  of  intrusive  bodies  of  the  gabbro  found  in  the 
same  district. 
